Silver alloys



Patented Nov. 15, 1938 UNITED STATES PATENT OFFICE SILVER ALLOYS Kenneth L. Emmert, Indianapolis, Ind., assignor to P. R. Mallory & Co., Inc., Indianapolis, Ind., a corporation of Delaware No Drawing.

Application September 11, 1937,

Serial No. 163,435

Claims.

contact resistance over long periods of operation.

A still further object is to provide a new contact material which can be used under severe electrical conditions without sticking.

It is another object of the invention to produce a contact material having as good electrical characteristics as fine silver, and which has a lesser tendency than silver to produce metal transfers during contact operation.

It is a further object of the invention to pro vide a contact capable of operating continuously at high frequency at heavy current values without objectionable contact metal transfer.

Other objects of the invention will be apparent from the following description taken in connection with the appended claims.

The present invention comprises a combination of elements, methods of manufacture, and the product thereof, brought out and exemplified in the disclosure hereinafter set forth, the scope of the invention being indicated in the appended claims.

While a preferred embodiment of the invention is described herein, it is contemplated that considerable variation may be made inthe method of procedure and the combination of elements, without departing from the spirit of the invention.

The present invention relates to an alloy of silver, copper, cadmium and nickel of improved characteristics. It is contemplated that this alloy may be of general utility in applications where other alloys are now used. However it is believed that its principal applicationswill be for electrical purposes and especially for electric contacts.

In this aspect my invention relates to an improvement in the contact material set forth in my United States Letters Patent No. 2,080,811, 50 issued May 18, 1937, which describes contact members of silver, cadmium and nickel. I have discovered that I can improve this alloy still further by adding considerable amounts of copper to it. This also results in a more economical alloy.

The alloy of the present invention may have its component ingredients present in the following permissible range of proportions by weight:

Per cent Nickel 0.1 to 5 Cadmium 0.5 to 25 Copper 0.5 to 35 Silver Balance.

In most cases it will be desired to have the alloy ingredients present in the following preferred percentage range:

Per cent Nickel 1 to 3 Cadmium 2 to 20 Copper 5 to 15 Silver Balance.

A preferred contact material has the following composition:

Per cent Copper 6 V Cadmium 18 Nicke'l 2 Silver -1 74 A second preferred composition is:

. Per cent Copper 28 Nickel 2 Silver 63 Usually the addition of copper to a silver base material has been found to be objectionable because during operation the contact surface has a tendency to oxidize. It has heretofore been found, for example, that the contact resistance of silver alloys containing copper increases much more rapidly than in silver alloys without copper. This was due to the fact that copper oxide has a very high specific resistance while silver oxide has a much lower specific resistance. Furthermore, the silver oxide dissociates very rapidly when heated to elevated temperatures, and forms so called metallic contact bridges.

It is remarkable, therefore, that the contacts of the present invention, although containing a considerable proportion of copper, do not show this rapid increase of contact resistance in operation. This is believed to be due to the presence of the nickel and cadmium in the alloy.

Contacts of the present invention are suitable for use as make and break contacts for controlling either A. C. or D. C. circuits. They may be used in bars of the same composition or an individual contact of this composition may be used with a co-operating contact of entirely different composition.

The combination of the elements, copper, cadmium, nickel and silver has resulted in a material which has not only superior electrical contact characteristics, but which shows greatly improved mechanical properties. A large number of tests were made in which materials of different compositions were severely cold worked and then annealed. In the manufacture of electrical contacts, a cold heading operation is used to form contact rivets consisting of a head and shank. The amount of cold work that is received in this operation amounts to at least 50-75%. Furthermore, the wire which is used for this cold heading operation is usually required to be quite hard. After such heavy cold work most materials have a tendency to soften at a relatively low temperature and to recrystallize. In this respect I have found that my new composition is far superior to the alloys of the prior art. For instance, the annealing temperature of my new alloy is approximately l50-200 C. above that of an alloy containing cobalt instead of the nickel.

It is of great importance that alloys which are used for electrical contacts be very homogeneous and uniform, and for that reason, it is necessary that in melting, the material must not segregate, but be uniformly mixed and well distributed. Segregation causes differences in mechanical properties, differences in the electrical resistance and it is particularly harmful as far as electrical conta t performance is concerned. In this respect I have found that nickel has a marked advantage over the other metals of the iron group.

I have made a large number of experiments with the metals of the iron group, namely iron, nickel and cobalt. Of these three metals, iron and cobalt are rather similar in their behavior and in their mode of alloying with silver or copper. Nickel, for instance, will form a complete series of solid solutions with copper. On the other hand iron and cobalt have a very limited solid solubility in copper. My experiments have shown that their solid solubility in silver is still less. As a matter of fact, I have found it extremely difficult to obtain silver alloys of the nature described, containing appreciable quantities of either iron or cobalt. These ditnculties are entirely overcome if nickel is substituted for cobalt. I have found particularly that in alloys consisting of nickel, cadmium, copper and silver I can produce a grain size which is extremely small and uniform. The nickel hardens the alloy whereby it is highly resistant to mechanical wear, as well as to electrical wear.

Silver alloys in general are very susceptible to sulfiding or tarnishing. This is particularly harmful if these alloys are used in chemical plants, where it is impossible to prevent a sulfur atmosphere. Most silver alloys when used for contacts where they are exposed to sulfurous atmospheres develop a very high contact resistance and the contacts will overheat and finally fail.

With the present alloy which contains a high percentage of cadmium, in addition to copper and nickel, I have found that the suflding tendency, as well as the general tarnishing tendencies, are greatly reduced, and the alloys can therefore be used in applications where other silver base materials have previously failed. The present alloy has been found to be highly satisfactory for use on equipment of intermittent operation, where the contacts are subjected to sulfur fumes.

The novel contacts disclosed herein have little tendency toward metal transfer and metal build up on the contact surfaces and very little tendency of the contacts to fuse together. It is thought that this is due principally to the presence of cadmium. Cadmium is an element which has a rather low boiling point and if a local overheating occurs on the contact, cadmium oxide is formed on the surface, which will prevent sticking together of the metallic silver particles, because they are surrounded by a. thin layer of cadmium oxide.

Comparative tests have been made on contacts of the preferred compositions given above in comparison to contacts of fine silver and coin silver. In the tests the contacts were operated at a frequency of approximately 1500 operations per hour and made to carry 1% amperes at 110 volts D. C. The contacts of the present invention were still functioning satisfactorily at over 100,000 operations. Coin silver operating under the same condition failed at less than 70,000 operations, with fine silver failing at less than 1500.

When operated on voltage regulators, such as used in the regulation of automotive generators, the material of the present invention, operating against a. high silver alloy of a different composition, maintained perfect regulation. This operatfon at frequencies between 50 and 400 cycles, for periods of in excess of 500 hours, gave contact resistance values of extremely low order.

It is contemplated that small proportions of other materials which do not substantially alter the characteristics of the alloy, such as impurities, for instance, may be present in the alloy of the present invention and are intended to be within the scope of the claims.

While the present invention as to its objects and advantages has been described herein as carried out in specific embodiments thereof, it is not desired to be limited thereby but it is intended to cover the invention broadly within the spirit and scope of the appended claims.

What is claimed is:

1. An alloy composed of 0.1 to 5% nickel, 0.5 to 25% cadmium, 0.5 to 35% copper and the balance substantially all silver, said alloy being characterized by less tendency to oxidize or sulfide than a straight silver-copper alloy and greater homogeneity than an alloy of similar proportions wherein iron or cobalt is utilized instead of nickel.

2. An alloy composed of l to 3% nickel, 2 to 20% cadmium, 5 to 15% copper and the balance substantially all silver, said alloy being characterized by less tendency to oxidize or sulfide than a straight silver-copper alloy and greater homogeneity than an alloy of similar, proportions wherein iron or cobalt is utilized instead of nickel.

3. An electric contact member formed of an alloy composed of 0.1 to 5% nickel, 0.5 to 25% cadmium, 0.5 to 35% copper' and the balance substantially all silver, said alloybeing characterized by less tendency to oxidize or sulfide than a straight silver-copper alloy and greater homogeneity than an alloy of similar proportions wherein iron or cobalt is utilized instead of nickel, and said contact member having longer contact life than similar members of fine silver or com silver.

4. An electric contact member formed of an alloy composed of 1 to 3% nickel, 2 to 20% cadsilver-copper alloy and greater homogeneity than an alloy of similar proportions wherein iron or cobalt are utilized instead of nickel, and said contact member having longer contact life than similar members of fine silver or coin silver.

-5. An electric contact member formed. of an alloy composed of 2% nickel, 7% cadmium, 28% copper and 63% silver.

' KENNETH L. EMMERT. 

